Telephone substation set



. K; S. JOHNSON TELEPHONE SUBSTATION SET Filed Got. a, 1917 /n WM M r.-

. W M y Patented Apr. 17, 1923.

UNlTE D STATES PATENT oral cs.

KENNETH S. JOHNSON, 10F JERSEY CITY, NEW JERSEY, ASSIGNOR TO WESTERN ELEC- TRIO COMPANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK.

TELEPHONE SUBSTATION SET.

Application filed October 8, 1917. Serial No. 195,364.

To all whom 2'25 may concern Be it known that I, KENNETH S. JOHNSON, a citizen of the United States, residing at Jersey City, in the county of Hudson and 5 State of New Jersey, have invented certain new and useful Improvements in Telephone Sub-station Sets, of which the followingis a full, clear, concise, and exact description.

This invention relates to telephone substation sets and in particular to so arranging and proportioning the elements of a telephone substation local battery set, which consists of a receiver, transmitter and a transformer, that the set will be of maximum theoretical efliciency for two-way signaling efiiciency irrespective of what values are assigned to the resistance of the transmitter, the set impedance and the receiver impedance. By maximum efiiciency in a two-way signaling system as exemplified in a telephone substation is meant the condition wherein, assuming reactances to act as pure resistances, in receiving, fifty per cent of the energy received in the substation is delivered to the receiver, and, in transmitting, fifty per cent of the energy generated in the transmitter is delivered to the line. A. full discussion of two-way signaling efliciency in telephone substations will be found in the patent of George A. Campbell, No. 1,254A74c, dated January 22, 1918. A particular object is the fulfilment of the above conditions where the value assigned to the set impedance is large;

These objects are attained in substations of the form diagrammatically shown in the accompanying drawings. wherein Fig. 1 illustrates one embodiment of the invention; and Fig. 2 illustrates a variant but fundamentally equivalent form. The form of Fig.

1 would be assumed by the circuit of Fig. 2 in case certain conditions were imposed upon the elements of the substation as hereinafter set forth. Fig. 1 shows one different possible location for the local battery. Fig. 1

shows another possible location for the battery in case a permanent magnet receiver is used. Fig. 2 shows a variation of the circuit of Fig. 2.

R ferring specifically to Fig. 1, numerals 1, 2 and 8 represent three coils or portions of the winding of an auto-transformer. Aroui'id portion 1 is connected a transmitter 4, around portions 1 and 2 is connected a line 6, and around portions 1, 2 and 3 is connected the receiver The windings of the coil are so arranged that currents passing, as shown by the arrows,produce a se ries aiding effect in the transformer as a whole. Battery 7 is placed in series with both the transmitter and receiver.

The battery may be placed in series with the coil 1 as indicated in Fig. 1. A condenser 8 may then be used to prevent battery current flowing'in the line. In case a permanent magnet receiver is used, the battery may be placed in effective series with the transmitter 4; only, as shown in Fig. 1. Fig. 2 differs from Fig. 1 intliat the points of connection of receiver 5 and line 6 to the transformer are interchanged.

A substation circuit, arranged as herein set forth, has the unique advantage that when using a neutral receiver,- it can be designed so as to be ideally cfficiennboth from an alterating current standpoint and from a direct current standpoint. A neutral receiver isone which has a normally unmagnetizediron core which ismagnetized by battery current in order to place it in condition for effective reception of voice currents. Neutral receivers are adapted for the arrangements illustrated in Figs. 1, 2, 1 and 2 Thus, assuming as given, which is usually the case, the permissible voltage ofthe battery and the ampere turns necessary to properly magnetize the neutral receiver for maximum efliciency; also assuming that the resistance of the windings 1, 2 and 3 to direct current is negligible, we may determine at once the proper direct current resistance for the neutral receiver. The characteristics of any given receiver by calculation or experiment can be determined, so that its impedence at talking frequencies can be assumed as known when its D. C. resistance has been determined. Then. also having given the set impedance, the transmitter resistance, and the energy ratio,

which is the ratio of energy deliv'ered'to the transmitter to that delivered to the re ceiver when receiving, and furthermore, making the assumption that the transformer l, 2 and 3 is ideally eflicient, and that the impedance of the various elements to current of talking frequency acts as ohmic resistance, which assumptions are sufiiciently nearly true in practice, it can be shown that in such a circuit as Fig. 2:

resents the telephonic current through the receiver 1n receiving, and A, B and C represent the lmpedances of windings 1, 2 and Z =RT B my (1) 3 respectively. The radicals 8 RA T( /K+ /E) V5 and y? A R A A I 2 l /A-t /B) T will therefore represent ratios between E F I number of turns. The positive values of ,1 (3) the radicals should, in general be used. A Formula follows directly from formula (2) while formula (4;) is derived from tvw- (1) and (2). Formulae 1 and 2 may be dey rived as follows: wherein, Assume an electromotive force e in the S t P d line 6 and currents I I 1 1 I and I R recelver lmpedance, flowing in the directions indicated by the T :transmrtter impedance, arrowsin Fig. 2, and that the currents I L; y :energy ratio and L; all tend to produce flux in the same I direction. From Kirchhofls first law, i TRl 10:11,,- IB::IL-IR, and. IA:ILIR IT. Applying K1rchhofi"s second law, we get: where I represents the telephonic current by going around the mesh containing L, B through the transmitter in receiving I repand U (I) e ILL ILG (IL IR)MBC (IL n r) Ac IRR by going around the mesh containing T and A 11) IL IR o or Io s IL Ac T by going around the mesh containing A, B and R I (III) (I I IQA (I IQM I M (I I )B (I I IQM I M 1 R (c) Rearranging these equations We have, respectively:

IL(L O ac ac? IR(R ac M110) r MAC) e IL(A+LJAB +MAC) u( A- 1V[AB) +IT( AT) 0 I (A+B+2M +M +M +I (A-B2M -R) +I (AM =0 (f) Solving the equations ((1), (e) and (7) simultaneously, We get:

IR l( MAB) (A MAB ho) (A T) (A ZMAB Ac MBC 1 (g) IL: e[(A+M (A +TI))(A +B 2M +Ri] (h) IT 6[(A +MAB) (R MAC %c) +MAC(A B ZIVIAB ll In all of which we have:

D [L+C +M +M ][(A +M (A+T) (A +B 2M B+R)] +MAB ACl[( +MAB) MAC nd MAC(A B ZMAB 5 B 2MAB MAC T) lu: isc) NIAC IVIAB 1 Since in an ideal transformer, i. e., one Making these substitutions and simplifying. which neither stores nor absorbs energy, we equalllons (9 )1 and become: have no flux leakage, I eT[(1,/K+ /BY-i- /fiM/K-k #3)] t R u D MAB: VAB I T /K F /B" +AR (Z) L MAC n 1 -s I eR /A( /A+ /B+ /C) M /Bo T e? (m) Note that in obtaining equation (Z), equation (it) first becomes,

-a-AR-ALBT-QTMg E I Since'the transformer is assumed to be ideal, theself'impedances A and B and the mutual impedance M are of the order or" infinity, thequantity re which is finite is therefore or negligible value as compared with the first" four quantities and maybe dropped.

By definition r Hence, from equations (is) and(m) we get:

or formula (2). above, Assuming that L O, or in other words that c is the terminal voltage acrossthe set:

which may be Written as in formula (,Z) above.

Formulae (3) and (4) show that for any given value of y, if T and R are determined,

the winding ratio may be adjusted tomake Z any desired value. The value of 3/ ordinarily desirable is approximately unity,.which value is the condition for maximum efliciency.

If the receiver be of relatively high impedance. to speech currents, theratio will be zero or negative. By combining'the formulae (3) and (4), it will be seen that the negative value will occur when R Z r +1) or R 2Z when yzl. The physical embodiment of this condition is shown in Fig. 1 where the receiver is connected across an three of the transformer windings and the line across 1 and 2 only. In case the wins Gran ma am are, or whi h th Physica int nr'etat n is th t l andre'eeiver are connected at each of their respective terminals to the same point in the transformer. The substation arrangement of Fig. 2 has been found to be of practical advantage where a substation set of unusually high total impedance is des1rable, but with the highest efliciency under such circumstances.

The design formulae for Fig. 1 may be derived in a similar manner to that outlined above for Fig. 2. Assuming the reference characters to be defined as above, it can be readily shown that in sucha clrcuit as Fig. 1 I =m' a fA- h Atw t 1 (/g i' I i A R rm T (u) 5 With R, T, and y given it Willbe apparent that Z the impedance of the set may be given any desired value by a proper proportioning of the three windings. One way it can be done for example is to vary the ratio of B to C, keeping B plus C constant. Underthese conditions it will be seen from equation that B l-C being constant 3/ will not vary when the ratio of B to C is changed; and from equation (7*) that Z,

will change when the ratio is changedsince only Boccurs in the numerator while B-l-C occurs in the'denominator." Z may therefore be adjusted ratio. I

With these arrangements; assuming the use of a neutralreceiver and a single transformer, a set can 'be designed to be of maximum possibletheoretical efiiciency with any assigned values of transmitter resistance,

\ Without changing the energy energy ratio and set impedance. Although reference is made herein to a neutral receiver,

itshould be notedthat the invention in its generic spects not limitedto the use of such a receiver. Furthermore'the invention is not limited as use'in local battery sets.

N is

Figures 1 and l typify a battery location suitable for the arrangement of Fig. 2 as well as Fig. 1. In the practical use of any set herein described, a suitable ringing generator and bell or other signaling means may be bridged across or otherwise suitably connected to the line in a manner well-known in the art, hence these features are not necessary to be described herein. A condenser 8 may be placed in the line in the usual manner as shown in Fig. l in order to prevent the battery 7 sending current through the line. The coil may be divided into two parts, 3 and 3", as illustrated in Fig. 2. Under certain circumstances it might be desirable to ground the transformer at the electrical mid-point of its total turns, in which case 8 and 3 would be so proportioned as to make the mid-point exactly coincide with one of the tap out points between. 3 and l, or 1 and or 2 and The total number of turns of 3 and 3 would be equal to the turns of 3. This arrangement is the full equivalent in respect to the invention herein claimed to that of Fig.2.

It will be noted from the form of equation (1), that the expression for the set impedance is a fraction, the numerator of which involves the product of the receiver and transmitter impedances and the denominator involves their sum. This shows that the instruments are effectively in parallel. It follows that if the set be designed so that 3/ is approximately unity, the energy of received signals will divide substantially equally between the receiver and the transmitter.

hat is claimed is:

1. A telephone circuit including three elements which consist of a line, a receiver and a transmitter, a transformer associated with said elements, said transmitter being connected. across a coil of said transformer. said receiver being connectedacross said coil and another coil of said transformer. said line being connected across all the coils of said.

transformer, said coils being so wound and arranged that current passing through them from one extreme electrical terminal to the other extreme electrical terminal of said transformer produces a series aiding effect in said elements has a series aiding inductive effect in said transformer as a whole.

3. A telephone circuit having a three coil auto-transformer and three elements consisting of a receiver, a transmitter and a line, said transformer having four tap out points, said receiver, transmitter and line each having terminals connected to said transformer at two tap out points, all of said elements having one common terminal and each having an individual terminal, said coils being wound so that'current passing through each one in a direction away from said common terminal of said elements has a series aiding inductive effect in said transformer as a whole. the parts of said substation being so proportioned that the substation is of approximately maximum efficiency.

4. A telephone substation set comprising a transformer, a neutral receiver, a transmitter, a local battery, a series circuit including said battery, said receiver and at least a portion of said transformer, a second series circuit including said transmitter, said battery and at least a portion of said transformer, connections including at least a portion of said transformer for connecting the substation set to a line, said-portions in said first and said second circuits and in said connections having a relative ratio of turns dependin i u on the im )edances of said transmitter g p l and said receiver to make the energy ratio (y) approximately unity in receiving signals from said line. b 5. A telephone substationset comprising a transformer having three coils. a neutral receiver, a transmitter, a local battery, :1 se ries circuit including said battery, said receiver and atleast one of said coils, a second series circuit including said battery, said transmitter and at least one of said coils, con nections including at least two of said coils for connecting the substation set to a line, said three coils having a relative ratio of turns dependent upon the impedances of said transmitter and receiver to make the energy ratio (11 approximately unity in receiving signals from said line.

6. A telephone circuit including three elements constituting a line, a receiver andv a transmitter together with a three coil autotransformer, one of said elements being connected across one coil of said transformer, a second of said elements being connected. across two coils of said transformer, and a third of said elements being connected across three coils of said transformer, said coils being so arranged that current passing through each of said coils in a direction from one extreme end of said transformer to the other extreme end thereof, produces a series aiding effect in respect to the voltage induced across said extreme ends.

7. A telephone circuit comprising a receiver, a transmitter, a line and a three coil transformer, said receiver, transmitter, and line being connected across the terminals of the coils of said transformer, said coils being so wound that in receiving the energy is approximately equally distributed be-,

tween the receiver and the transmitter, the impedance of said receiver being appreciably in excess of the impedance of said transmitter.

8. An auto-transformer having three windings, and four tap out points, and three elements comprising a transmitter, a receiver, and a line, each having terminals connected to said tap out points, said con nections having substantially no impedance to alternating currents, two of said elements having a common terminal.

9. An auto-transformer having three windings, and four tap out points, and three elements comprising a transmitter, a receiver and a line, each having terminals connected to said tap out points, said con nections having substantially no impedance to alternating currents, two of said elements having a common terminal, said receiver and said transmitter being effectively in parallel with respect to received currents.

10. A telephone circuit comprising four elements consisting of a three coil autotransformer, having two terminal and two intermediate tap out points, a receiver, a transmitter and a line, said three last mentioned elements each having two terminals connected to said transformer at a tap out point, three of said four elements having a common terminal, said coils being wound so that current passing through each one in a directionaway from one end of the transformer terminals has a series aiding effect in said transformer as a Whole.

11. A telephone circuit comprising four elements consisting of a three coil autotransformer having two terminal and two intermediate tap out points, a receiver, a transmitter and a line, said three last mentioned elements each having two terminals connected to said transformer at a tap out point, three of said four elements having a common terminal, said transformer being so wound that the impedance of the set viewed from the line is appreciably greater than the impedance of the line.

12. A substation circuit comprising a transmitter and a receiver, connections from said instruments to a line, said instruments being connected effectively in parallel with each other with respect to signaling currents from said line, said connections comprising an autotransformer between at least one of said instruments :and said line, a portion of a winding of said transformer being connected in shunt to said'line with respect to said receiver.

13. A substation circuit comprising a transmitter, a receiver and a transformer for inductively coupling at least one of said instruments to a'line and connections, adjusted to divide the energy of the re ceived signaling currents approximately equally between said receiver and transmitter, for connecting said transformer, receiver and transmitter with said line in such a manner that said instruments are efiectively in parallel with said line, a portion of the winding of said transformer being connected in shunt to said line with respecit to said receiver.

In witness whereof I hereunto subscribe 

